Electric rotary machine having superconducting rotor

ABSTRACT

An electric rotary machine (for example, a dynamoelectric machine) having a superconducting rotor is disclosed in which an outer shielding member for protecting a superconducting field winding from the influence of the magnetic flux from the stator side and for interrupting heat radiated from the normal temperature side is made of a nickel alloy containing not more than 0.3% carbon, not more than 1% silicon, not more than 2% manganese, not more than 1.5% titanium, from 2 to 8% aluminum, from 8 to 40% copper, and not less than 55% nickel for the balance by weight. The nickel alloy has a structure that a γ&#39;-phase precipitation is formed by aging in an austenitic matrix, and is non-magnetic at 20° C.

This is a continuation of application Ser. No. 467,808, filed Feb. 18,1983 now abandoned.

The present invention relates to electric rotary machines such asdynamoelectric machines, and more particularly to an electromagneticshielding body of the normal temperature used in a superconductinggenerator.

In general, a superconducting rotor is used in a superconductingcondition in which a field winding is kept at an extremely lowtemperature less than 20° K. so that the resistance of the winding maybe greatly reduced. The electric rotary machines include an electricmotor, a generator, and a rotary phase modifier.

The rotor of a resolving-field type superconducting generator, which isone of the superconducting generators, has a structure wherein multiplexhollow-cylinders are coaxially disposed one within another. In moredetail, the rotor includes an outer electromagnetic shielding body, aninner electromagnetic shielding body (kept at a temperature which isabout 50° C. higher than the temperature of liquefaction of helium), asuperconducting coil cover, a superconducting coil bind, asuperconducting coil, a torque tube for mounting thereon thesuperconducting coil, a helium path for cooling, a shaft, a current leadwire, liquid helium, and a liquid helium supply pipe arranged in theorder described from the outside. When the rotor is rotated, the liquidhelium is pressed against the inner wall of the torque tube by thecentrifugal force, and thus has a cylindrical shape. The inside of theinner shielding body and that of the outer shielding body are kept atvacuum.

In a large-capacity superconducting generator, a current flowing throughthe armature winding changes when a fault or accident occurs in a powertransmission system. In this case, if the rotor is not provided with theabove-mentioned shielding bodies, a damping force is applied to therotor due to the electromagnetic interaction between a magnetic fluxgenerated by the armature winding and a field current. Thus, therotational speed of the rotor is decreased, the rotor is put in anasynchronous state. When the rotor is put in the asynchronous state, thearmature current changes more remarkably, and an excessive driving forceand a damping force are alternately applied to the rotor. This resultsin the fatal damage to both of the power transmission system andgenerator.

The electromagnetic shielding bodies are used to prevent the rotor frombeing put in an asynchronous state, and to prevent a magnetic fluxcomponent caused by the change in the armature current from linking thearmature and field windings. That is, the magnetic flux component isconverted by the shielding bodies into eddy currents flowing therein,and thus the flux density inside the shielding bodies is attenuated. Themagnetic flux generated by the armature winding has a frequencycomponent of 120 Hz due to the rotation, and a low-frequency componentof 0.5 to 2 Hz due to irregularities in rotation of the rotor. Theformer and latter components are cut off by the outer and innerelectromagnetic shielding bodies, respectively. At this time, owing tothe interaction between the magnetic flux generated by the armaturewinding and the eddy current flowing in the outer shielding body, arotational damping force by the irregularities in rotation and a strongelectromagnetic force are applied to the outer shielding body.

Accordingly, a material for making the outer shielding body is requiredto be excellent in conductivity and high in mechanical strength, andfurther required to be non-magnetic for the following reason. Surely, avery high flux density can be obtained by the superconducting coil.However, when a ferromagnetic material is interposed between thesuperconducting coil and armature winding, an available magnetic flux isreduced due to the magnetic saturation of the ferromagnetic material.

It has been proposed that the outer shielding body is formed in atwo-layer structure in which a non-magnetic copper alloy having a largeconductivity and a non-magnetic steel having a high mechanical strengthare joined together by explosive bonding in the prior art publicationsof U.S. Pat. Nos. 4,039,870 and 4,171,494. In the shielding body formedin the two-layer structure, however, owing to the use of welding in themanufacturing process, exfoliation may occur between the two layers anda weld crack may be generated in a welded portion of the layers.Further, these defects may proceed in the course of rotation, and thusthere is the danger of damage to the shielding body. Therefore, it isunfavorable from a practical point of view to use a composite structureand a welding technique in fabricating the outer shielding body.

Further, it has been known that precipitation hardening aluminum alloyand copper alloy are non-magnetic and have good conductivity at normaltemperature. However, these alloys show a yield strength of 50 kg/mm² orless with a 0.2% offset at normal temperature, that is, the 0.2% proofstress of these alloys at normal temperature is equal to or less than 50kg/mm². In a superconducting generator with a capacity of 50 MVA ormore, the electromagnetic shielding body of normal temperature isrequired to have a 0.2% proof stress of 60 kg/mm² or more. Therefore, itis impossible to make the shielding body of aluminum alloys or copperalloys.

An object of the present invention is to provide an electric rotarymachine having a superconducting rotor in which an outer electromagneticshielding body included in the superconducting rotor can solve theabove-mentioned problems of the prior art, and is ductile, non-magnetic,with good conductivity and high mechanical strength at normaltemperature.

In order to attain the above object, according to the present invention,there is provided an electric rotary machine having a superconductingrotor, in which the superconducting rotor comprises a driving shafthaving at an end thereof a flange portion, a hollow shaft confrontingthe driving shaft with a gap therebetween and having a flange portion, atorque tube connected between the flange portions, a field windingprovided on an outer peripheral surface of the torque tube, a coolantpool formed in the torque tube, coolant supply means for supplying acoolant to the coolant pool through the hollow shaft, an inner shieldingmember formed of a cylindrical non-magnetic body and provided so as tosurround the field winding, a cylindrical outer shielding memberdisposed so as to surround the inner shielding member and connectedbetween the flange portions, coolant discharge means for collecting thecoolant from the coolant pool through the hollow shaft, and a power leadpassing through the hollow shaft for supplying the field winding withelectric power, and in which the outer shielding member is made of anon-magnetic nickel alloy containing not more than 0.3% carbon, not morethan 1% silicon, not more than 2% manganese, not more than 1.5%titanium, from 2 to 8% aluminum, from 8 to 40% copper, and not less than55% nickel for the balance by weight, said alloy having such a structurethat a γ'-phase precipitation is formed by aging in an austenitic matrixand is non-magnetic at 20° C.

According to the present invention, a member which is large inmechanical strength and low in resistivity, is used as the outershielding member. Accordingly, the outer shielding member can withstandany centrifugal force and any electromagnetic force which may begenerated in a large-sized electric rotary machine, and therefore thedamage to or deformation of the shielding member due to an accident canbe prevented.

The present invention will become apparent from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a graph showing the relation between copper content and Curiepoint for alloys according to the present invention;

FIG. 2 is a graph showing the relation between aluminum content andresistivity at 20° C. for the alloys;

FIG. 3 is a graph showing the relation between aluminum content and 0.2%proof stress at 20° C. for the alloys;

FIG. 4 is a graph showing the relation between aluminum content andcopper content for the alloys; and

FIG. 5 is a sectional view showing an embodiment of a superconductingrotor according to the present invention.

After the extensive investigation of nickel alloys, the presentinventors have found the previously-mentioned novel nickel-copper alloywhich is high in mechanical strength, large in electrical conductivity,and non-magnetic.

The Curie point of a nickel-copper binary alloy is low as the coppercontent thereof is larger, and the alloy is non-magnetic at normaltemperature for a copper content exceeding 15%. Further, the resistivityof the alloy increases as the copper content is larger. Since the outerelectromagnetic shielding body is kept at normal temperature, it ispreferable that the outer shielding body has a resistivity of 70 μΩ.cmor less at normal temperature. A nickel-copper alloy whose coppercontent is not more than 40%, has a resistivity of 70 μΩ.cm or less.

The mechanical strength of nickel-copper binary alloy is generally low.In order to improve the mechanical strength of the alloy byprecipitation hardening without increasing the resistivity thereofgreatly, various elements have been added to the alloy. Of the elements,aluminum has produced the most excellent result. That is, when aging iscarried out at a temperature of 450° to 650° C. for a nickel-copperalloy containing an appropriate amount of aluminum, an austenitestructure containing a γ'-phase (of Ni₃ Al type) is formed. Thus, themechanical strength of the alloy is greatly increased. Further, theaddition of aluminum is effective for lowering the Curie point of thealloy.

A nickel alloy suitable for use in an outer electromagnetic shieldingbody according to the present invention preferably contains from 0.05 to0.25% carbon, from 0.01 to 0.5% silicon, from 0.01 to 1.5% manganese,from 2.5 to 6% aluminum, from 9.2 to 15% copper, and not less than 60%nickel for the balance by weight. Further, it is preferable that theabove alloy contains from 0.1 to 0.6% titanium by weight.

The composition range of the nickel alloy for making an outer shieldingbody according to the present invention is limited as mentioned above,for the following reasons. Carbon is added to the alloy for the purposeof solution strengthening. However, when carbon is added too much, notonly the resistivity of the alloy is increased, but also titaniumcarbide TiC is precipitated in the alloy. The precipitation of TiCdeteriorates the machinability of the alloy. Accordingly, it ispreferable that the carbon content of the alloy is not more than 0.3%.It is especially preferable that the carbon content lies in a range from0.05 to 0.25%.

Silicon is added to the alloy as a deoxidizer in melting the alloy. Itis desirable that the silicon content of the alloy is not less than0.01%, but the silicon content is required to be not more than 1%. Inorder to obtain alloys to have a good hot-workability, high toughnessand a large electrical conductivity, it is preferable that the siliconcontent be not more than 0.5%.

Manganese is added to the alloy as a deoxidizer and a desulfurizer inmelting the alloy. It is desirable that the manganese content of thealloy is not less than 0.1%, but the manganese content is required to benot more than 2%. In order to maintain the high conductivity of thealloy, it is preferable that the manganese content is not more than1.5%. It is especially preferable to put the manganese content in arange from 0.1 to 0.5%.

Aluminum produces a γ'-phase (of Ni₃ Al type) in a matrix by aging toreinforce the alloy, and moreover lowers the Curie point of the alloy.It is necessary for the aluminum content of the alloy to be not lessthan 2%. However, when the aluminum content exceeds 8%, thehot-workability, toughness and electrical conductivity of the alloy aredeteriorated. It is especially preferable that the aluminum content liesin a range from 2.5 to 6%.

Copper lowers the Curie point of the alloy without increasing theresistivity thereof greatly. It is necessary for the copper content isnot less than 8%. However, when the copper content exceeds 40%, theconductivity and mechanical strength of the alloy are reduced. Thecopper content lies preferably in a range from 12 to 33%, and morepreferably in a range from 9.2 to 15%.

Titanium produces titanium carbide in the alloy and reinforces the alloyremarkably. The titanium carbide does not only reinforce the alloy butalso makes crystal grains small. Accordingly, the hot-workability andtoughness of the alloy are greatly improved. Further, when a very smallamount of titanium is added to the alloy, titanium acts as a veryeffective deoxidizer. The titanium content of the alloy is preferablyput in a range from 0.1 to 0.6%.

In the present invention, it is preferred to use a nickel alloysubstantially containing from 0.05 to 0.25% carbon, x% aluminum, y%copper, and the balance nickel, where the aluminum content x and coppercontent y lie within a composition range having as corners thereof acomposition A (containing 2% aluminum and 12% copper), a composition H(containing 2.5% aluminum and 15% copper), a composition I (containing8% aluminum and 15% copper), a composition E (containing 8% aluminum and10% copper), a composition J (containing 7.3% aluminum and 9.2% copper),and a composition K (containing 3.7% aluminum and 9.2% copper). Thus, anickle alloy can be obtained which is non-magnetic at 20° C. and has at20° C. a proof stress 60 kg/mm² or more and a resistivity of 70 μΩcm orless. It is preferable that the nickel alloy further contains from 0.01to 0.5% silicon, from 0.01 to 0.5% manganese and from 0.1 to 0.6%titanium.

A cylindrical outer shielding member according to the present inventioncan be formed in various manners. For example, a hollow cylinder havinga predetermined shape is made by casting, a ring is made by casting andthen the ring is shaped into a hollow cylinder by forging, or a plate isfirst made by forging and then the plate is bent into a semi-cylindricalshape, the facing edges of which are joined together by welding to forma hollow-cylinder. The hollow-cylinder thus formed is subjected to asolution treatment, and then the γ'-phase is formed by aging toreinforce the cylinder. The alloy may be made by melting in air orvacuum. It is especially preferable that electroslag remelting iscarried out for the above alloy.

The solution treatment is preferably carried out at a temperature of800° to 950° C., and the aging is preferably performed at temperaturesbetween 450° C. and 650° C. The aging is carried out at a plurality ofstages. For example, first, second and third age treatments areperformed at a temperature of 550° to 650° C., a temperature of 500° to600° C., and a temperature of 450° to 550° C., respectively. Themechanical strength of the cylinder is large and the aging time isshort, as the number of age treatments is larger.

As is apparent from the foregoing description, an outer shielding memberaccording to the present invention is not formed into a conventionaltwo-layer structure, but formed into a single alloy layer.

EMBODIMENT 1

Nickel alloys having carbon, silicon, manganese, titanium, aluminum,copper and nickel contents (in weight %) shown in the following Table 1were made by vacuum melting, and then a plate having a thickness of 15mm was made of each of the alloys by hot rolling at 750°-1100° C. Theplate was kept at 850° C. for a half hour and immediately thereaftercooled in water, to be subjected to a solution treatment. Then, theplate was placed in a furnace, to be kept at 620° C. for two hours andthen cooled in the furnace. Subsequently, the plate was kept at 565° C.for four hours and then cooled in the furnace. Further, the plate waskept at 510° C. for four hours, and then cooled in air. Thus, aging wascarried out for the plate. The Curie point, resistivity at normaltemperature, and 0.2% proof stress at normal temperature (namely, ayield strength producing a 0.2% permanent elongation at normaltemperature) were measured for each plate. The results of measurementsare also shown in the following Table 1.

                                      TABLE 1                                     __________________________________________________________________________                          Curie     0.2% proof                                    Sample                point                                                                             Resistivity                                                                         stress                                        No. C  Si                                                                              Mn Ti                                                                              Al                                                                              Cu Ni (°C.)                                                                      (μΩ · cm)                                                         (kg/mm.sup.2)                                 __________________________________________________________________________    1   0.15                                                                             0.2                                                                             0.2                                                                              0.4                                                                             2.3                                                                             27.0                                                                             69.75                                                                            -80 60    60                                            2   0.15                                                                             0.2                                                                             0.2                                                                              0.4                                                                             2.3                                                                             33.0                                                                             63.75                                                                            -90 60    60                                            3   0.15                                                                             0.2                                                                             0.2                                                                              0.4                                                                             3.5                                                                             27.0                                                                             68.55                                                                            -105                                                                              62    75                                            4   0.15                                                                             0.2                                                                             0.2                                                                              0.4                                                                             3.5                                                                             33.0                                                                             62.55                                                                            -90 63    70                                            5   0.15                                                                             0.2                                                                             0.2                                                                              0.4                                                                             2.5                                                                             15.0                                                                             81.55                                                                              0 47    64                                            6   0.15                                                                             0.2                                                                             0.2                                                                              0.4                                                                             2.5                                                                             27.0                                                                             69.55                                                                            -90 53    63                                            7   0.15                                                                             0.2                                                                             0.2                                                                              0.4                                                                             5.0                                                                             15.0                                                                             79.05                                                                            -30 52    87                                            8   0.15                                                                             0.2                                                                             0.2                                                                              0.4                                                                             5.0                                                                             27.0                                                                             67.05                                                                            -100                                                                              60    80                                            __________________________________________________________________________

Further, nickel alloys having carbon, silicon, manganese, titanium,aluminum, copper and nickel contents (in weight %) shown in thefollowing Table 2 were made by vacuum melting, and then a plate having athickness of 15 mm was made of each of these alloys by hot forging at atemperature of 750° to 1100° C. The plate was kept at a temperature of800° to 900° C. for one hour and immediately thereafter cooled in water,to be subjected to a solution treatment. Then, the plate was placed in afurnace, to be kept at 590° C. for 16 hours and then cooled in thefurnace. Subsequently, the plate was kept at 540° C. for six hours, andthen cooled in the furnace. Further, the plate was kept at 480° C. forsix hours, and then cooled in air. Thus, aging was carried out for theplate. The Curie point, resistivity at normal temperature and 0.2% proofstress at normal temperature were measured for each plate. The resultsof measurements are also shown in the following Table 2.

                                      TABLE 2                                     __________________________________________________________________________                          Curie      0.2% Proof                                   Sample                point                                                                              Resistivity                                                                         stress                                       No. C  Si                                                                              Mn Ti                                                                              Al                                                                              Cu Ni (°C.)                                                                       (μΩ · cm)                                                         (kg/mm.sup.2)                                __________________________________________________________________________    1'  0.01                                                                             0.2                                                                             0.2                                                                              0.4                                                                             5.8                                                                             31.2                                                                             62.19                                                                            <-196                                                                              68.7  115                                          2'  0.01                                                                             0.2                                                                             0.2                                                                              0.4                                                                             5.1                                                                             27.7                                                                             66.39                                                                            <-196                                                                              63.5  106                                          3'  0.01                                                                             0.2                                                                             0.2                                                                              0.5                                                                             6.7                                                                              9.2                                                                             83.19                                                                            -5   59.2  103                                          4'  0.01                                                                             0.2                                                                             0.2                                                                              0.4                                                                             4.8                                                                             13.8                                                                             80.59                                                                            -70  55.2  62                                           5'  0.01                                                                             0.2                                                                             0.2                                                                              0.4                                                                             5.4                                                                             13.5                                                                             80.29                                                                            -80  57.2  97                                           6'  0.01                                                                             0.2                                                                             0.2                                                                              0.4                                                                             5.9                                                                             10.8                                                                             82.49                                                                            -60  59.0  105                                          7'  0.15                                                                             0.2                                                                             0.2                                                                              0.4                                                                             4.4                                                                             14.8                                                                             79.85                                                                            -30  53.8  82                                           8'  0.15                                                                             0.2                                                                             0.2                                                                              0.4                                                                             4.0                                                                             14.3                                                                             80.75                                                                            -20  51.0  64                                           9'  0.16                                                                             0.2                                                                             0.2                                                                              1.2                                                                             2.7                                                                             13.8                                                                             81.74                                                                            -5   42.1  61                                           10' 0.15                                                                             0.2                                                                             0.2                                                                              0.8                                                                             3.9                                                                             10.4                                                                             84.35                                                                            -10  50.3  63                                           __________________________________________________________________________

FIG. 1 is a graph showing the relation between copper content and Curiepoint for the alloys listed in the Tables 1 and 2. Numerals in FIG. 1designate sample number. As is apparent from FIG. 1, the Curie point ofthe alloys is low as each of copper and aluminum contents is larger.

FIG. 2 is a graph showing the relation between aluminum content andresistivity for the alloys listed in the Tables 1 and 2. Numerals inFIG. 2 designate the sample number. As can be seen from FIG. 2, theresistivity of the alloys increases as each of aluminum and coppercontents is larger.

FIG. 3 is a graph showing the relation between aluminum content and 0.2%proof stress, for the alloys listed in the Tables 1 and 2. Numerals inFIG. 3 designate the sample number. It is known from FIG. 3 that theabove-mentioned 0.2% proof stress increases rapidly with increasingaluminum content and is not always affected by an increase in coppercontent.

FIG. 4 is a graph showing a range of aluminum and copper contents inwhich a nickel alloy is non-magnetic at 20° C. and has at 20° C. a 0.2%proof stress of 60 kg/mm² or more and a resistivity of 70 μΩ.cm or less.The above range was determined on the basis of the data shown in theTables 1 and 2. Referring to FIG. 4, a straight line connecting points Aand B, a straight line connecting points B and C, and a straight lineconnecting points G and A are drawn on the basis of the points A, B, Cand G each having a proof stress of 60 kg/mm². A straight lineconnecting points C and D and a straight line connecting points D and Eare drawn on the basis of the points C, D and E each having aresistivity of 70 μΩ.cm. Further, a straight line connecting points Eand F and a straight line connecting points F and G are drawn on thebasis of the points E, F and G each corresponding to a non-magneticalloy. In FIG. 4, the points A, B, C, D, E, F and G indicate acomposition containing 2% Al and 12% Cu, a composition containing 2.5%Al and 40% Cu, a composition containing 4.2% Al and 40% Cu, acomposition containing 8% Al and 20% Cu, a composition containing 8% Aland 10% Cu, a composition containing 7% Al and 8% Cu, and a composition4.5% Al and 8% Cu, respectively.

EMBODIMENT 2

10 kg of a nickel alloy having carbon, silicon, manganese, aluminum,titanium, copper and nickel contents (in weight %) shown in a Table 3was made by vacuum melting, and then a rod having a diameter of 30 mmwas made of the alloy by hot forging. Subsequently, electroslagremelting was carried out by using the rod as an electrode, and thus aningot having a diameter of 60 mm and a length of 230 mm was obtained. Aflux made by adding 2% TiO₂ to a mixture containing 40% CaF₂, 30% CaOand 30% Al₂ O₃ was used in the electroslag remelting. Further, theremelting was carried out at a current of 850 to 925 A, a voltage of 30to 34 V and a melting rate of 439 g/min. The ingot was shaped into a rodhaving a diameter of 30 mm by hot forging at the temperature of 750° C.to 1100° C. The rod thus formed was kept at 900° C. for a half hour andimmediately thereafter cooled in water, to be subjected to a solutiontreatment. Then, the rod was placed in a furnace, to be kept at 620° C.for two hours and then cooled in the furnace. Subsequently, the rod waskept at 565° C. for four hours and then cooled in the furnace. Further,the rod was kept at 510° C. for four hours and then cooled in air. Thus,aging was carried out for the rod.

The nickel alloy thus treated had a Curie point of -52° C., aresistivity of 53 μΩ.cm and a 0.2% proof stress of 78 kg/mm², andtherefore had all of characteristics required for an electromagneticshielding body which was provided in a superconducting generator.Further, according to the electroslag remelting in the presentembodiment, not only a refined alloy is obtained but also a large hollowingot can be formed. That is, an electromagnetic shielding body ofnormal temperature included in a superconducting generator having acapacity of 50 MVA or more, can be formed as a unitary forged body.

                  TABLE 3                                                         ______________________________________                                        C       Si    Mn       Al  Ti    Cu   Ni                                      ______________________________________                                        0.15    0.2   0.2      4.3 0.4   20.7 Balance                                 ______________________________________                                    

EMBODIMENT 3

10 kg of a nickel alloy having carbon, silicon, manganese, aluminum,titanium, copper and nickel contents (in weight %) shown in a Table 4was made by vacuum melting, and then a rod having a diameter of 30 mmwas made of the alloy by hot forging. Subsequently, electroslagremelting was performed by using the rod as an electrode, and thus aningot having a diameter of 60 mm and a length of 230 mm was obtained.The same flux as in EMBODIMENT 2 was used in the electroslag remelting.Furhter, the remelting was carried out at a current of 750 to 800 A, avoltage of 25 to 27 V, and a melting rate of 320 g/min. The ingot wasshaped into a rod having a diameter of 15 mm by hot forging at atemperature 750° to 1100° C. The rod thus formed was kept at 900° C. forone hour and immediately therefore cooled in water, to be subjected to asolution treatment. Then, the rod was placed in a furnace, to be kept at590° C. for 16 hours and then cooled in the furnace. Further, the rodwas kept at 540° C. for six hours, and then cooled in the furnace.Subsequently, the rod was kept at 480° C. for six hours, and then cooledin air. Thus, aging was carried out for the rod.

The nickel alloy thus treated had a Curie point of -20° C., aresistivity of 54 μΩ.cm and a 0.2% proof stress of 80 kg/mm², andtherefore had all of characteristics required for an electromagneticshielding body which was provided in a superconducting generator.

Furhter, according to the electroslag remelting in the presentembodiment, not only a pure alloy is obtained but also a large hollowingot can be formed. That is, an electromagnetic shielding body ofnormal temperature included in a superconducting generator having acapacity of 50 MVA or more can be formed as a unitary forged body.

                  TABLE 4                                                         ______________________________________                                        C       Si    Mn       Al  Ti    Cu   Ni                                      ______________________________________                                        0.15    0.2   0.2      4.2 0.4   14.6 Balance                                 ______________________________________                                    

As has been explained in the above-mentioned, according to the presentinvention, an outer shielding body can be made of a nickel alloy whichis excellent in all of the magnetic property, electric conductivity andmechanical strength.

EMBODIMENT 4

FIG. 5 shows, in section, a superconducting rotor of an A.C. generator.Roughly speaking, the superconducting rotor is made up of a rotor shaft,a field winding 5, and a coolant circulation path for maintaining thefield winding 5 at an extremely low-temperature below 20° K. The rotorshaft is of a split type, and includes a driving shaft 1 connected to aprime mover such as a gas turbine, a steam turbine or a water turbinefor transmitting a driving torque and a hollow-shaft 2 for passingtherethrough the coolant circulation path and a power lead explainedlater. These shafts 1 and 2 have respective flanges 1F and 2F at theirfacing ends, and confront each other with a predetermined distancetherebetween. A cylindrical outer shielding member 3 bridges the flanges1F and 2F and are fixed thereto, to unite the shafts 1 and 2 to onebody. A torque tube 4 is disposed inside the outer shielding member 3concentrically therewith, and also bridges the flanges 1F and 2F. Thefield winding 5 is disposed on the outside of the torque tube 4 totransmit a torque from the driving shaft 1. The outer peripheral surfaceof the field winding 5 is held by a non-magnetic holding sleeve 5H. Apower lead 5L passing through the hollow shaft 2 is connected to thefield winding 5, to supply thereto an electric power from an externalpower source. The torque tube 4 forms a coolant pool 7 havingsubstantially the same axial length as the field winding 5, togetherwith partitions 6A and 6B. A coolant supply pipe 8 passing through thehollow shaft 2 is extended into the coolant pool 7 so that an open endof the pipe 8 is placed in an axial portion of the coolant pool 7. Inletports 10A and 10B of cooling ducts 9A and 9B are provided in centralportions of the partitions 6A and 6B defining the coolant pool 7. Thecooling ducts 9A and 9B are disposed at both end portions 4a and 4b ofthe torque tube 4 along the inner periphery thereof. The cooling duct 9Afurther extends continuously along the inner peripheral surface of theouter shielding member 3, and is connected to a coolant discharge pipe11, together with the other cooling duct 9B. The coolant discharge pipe11 extends through the hollow shaft 2 to the outside of the rotor. Therotor shaft, field winding, and coolant circulation path are arranged asmentioned above.

In addition to the above-mentioned fundamental arrangement of thesuperconducting rotor, a cylindrical inner shielding member 12 isprovided around the field winding 5, in order to protect the fieldwinding 5 from the influence of the magnetic flux from the stator sideand to maintain the field winding at an extremely low temperaturewithout being affected by the heat radiation from the stator side. Toprotect the field winding 5, the inner shielding member 12 includes aninner shielding body 14 disposed within an annular space between thefield winding 5 and outer shielding member 3 coaxially with thesemembers 3 and 5, and inner and outer cylindrical reinforcing bodies 15Aand 15B closely fitted to the inner and outer peripheral surfaces of theinner shielding body 14. The inner shielding body 14 and the inner andouter reinforcing bodies 15A and 15B are supported by end portions 4aand 4b of the torque tube 4 through supporting end plates 16A and 16B.

According to the present invention, a hollow cylinder which is made ofone of the nickel alloys mentioned in EMBODIMENTS 1 to 3 and has asingle layer structure, is used as the outer shielding member 3 of thesuperconducting rotor, after having been subjected to solution and agetreatments.

Though not shown in the drawings, the driving shaft 1 and hollow shaft 2are rotatably supported by means of bearings, and a stator made up of astator core and a stator winding in the slot formed in the core isdisposed around the outer shielding member 3 with an appropriate air gaptherebetween.

Next, explanation will be made of the way for putting the field winding5 into a superconducting state.

First, liquid helium is fed into the coolant pool 7 as indicated bysolid lines with arrows, through the coolant supply pipe 8. In thisstate, the rotor is rotated. Owing to the resulting centrifugal force,liquid helium LH is spread over the entire inner peripheral surface of acentral portion of the torque tube 4 corresponding to the field winding5, as indicated by double-dotted chain lines. Consequently, the fieldwinding 5 is cooled from the inner side of the torque tube 4, and heliumboiled and vapourized through cooling is allowed to float in a centralportion of the coolant pool 7. Actually, the torque tube 4 is providedwith a number of small bores reaching the field winding 5, to allow theliquid helium LH in the coolant pool 7 to get into and out of the boresdue to the convection in the field of centrifugal force, thereby coolingthe field winding 5 to an extremely low temperature.

The gaseous helium floating in the central portion of the coolant pool 7is introduced into the cooling ducts 9A and 9B from the inlet ports 10Aand 10B, as indicated by single-dotted chain lines with arrows, to coolthe end portions 4a and 4b of the torque tube 4 and the outer shieldingmember 3. The gaseous helium is then discharged to the outside of therotor through the coolant discharge pipe 11, to be suitably collected.By feeding the liquid helium and circulating gaseous helium in theabove-mentioned manner, the field winding 5 is kept at the extremelylow-temperature, and the heat conduction to the field winding throughthe driving shaft 1, hollow shaft 2 and torque tube 4 is interrupted.The inside of the outer shielding member 3 is kept at vacuum, and theheat radiated from the stator side is insulated by the inner shieldingbody 14.

Further, the coolant supply pipe 8, coolant discharge pipe 11 and powerlead 5L pass through the hollow shaft 2, to be connected with respectivestationary parts on the outside of the rotor. More specifically, thoughnot shown in the drawings, the coolant supply pipe 8 and coolantdischarge pipe 11 are connected to the stationary parts through coolantsupply and discharge means, while the power lead 5L is connected to thestationary part through a slip ring.

The field winding 5 is put in and kept at the superconducting state byfeeding the liquid helium and circulating the gaseous helium in theabove-mentioned manner, and then excited to start the generator.

We claim:
 1. An electric rotary machine having a superconducting rotor,wherein said superconducting rotor comprises a driving shaft having atan end thereof a flange portion, a hollow shaft confronting said drivingshaft with a gap therebetween and having a flange portion, a torque tubeconnected between said flange portions, a field winding provided on anouter peripheral surface of said torque tube, said torque tube having acoolant pool therein, coolant supply means for supplying a coolant tosaid coolant pool through said hollow shaft, an inner shielding memberformed of a cylindrical non-magnetic body and provided so as to surroundthe field winding, a cylindrical outer shielding member disposed so asto surround the inner shielding member and connected between said flangeportions, said outer shielding member being a cylindrical single-layerbody, coolant discharge means for collecting said coolant from saidcoolant pool through said hollow shaft, and a power lead passing throughsaid hollow shaft for supplying said field winding with electric power,and wherein said outer shielding member is made of a non-magnetic nickelalloy containing 0.05 to 0.25% carbon, 0.01 to 0.5% silicon, 0.01 to0.5% manganese, 0.01 to 0.6% titanium, 2.5 to 6.0% aluminum, 9.2 to15.0% copper, and the balance nickel by weight, said alloy having such astructure that a γ'-phase precipitation is formed by hard-aging in anaustenitic matrix.
 2. An electric rotary machine having asuperconducting rotor as claimed in claim 1, wherein said outershielding member has a resistivity of 70 μΩ.cm or less and a 0.2% proofstress of 60 kg/mm² or more, at 20° C.
 3. An electric rotary machinehaving a superconducting rotor as claimed in claim 1, wherein saidcylindrical single-layer body is a body which has been made throughelectroslag remelting.
 4. An electric rotary machine having asuperconducting rotor as claimed in claim 1, wherein the alloy of theouter shielding member contains 4.2 to 5% aluminum.
 5. An electricrotary machine having a superconducting rotor, wherein saidsuperconducting rotor comprises a driving shaft having at an end thereofa flange portion, a hollow shaft confronting said driving shaft with agap therebetween and having a flange portion, a torque tube connectedbetween said flange portions, a field winding provided on an outerperipheral surface of said torque tube, said torque tube having acoolant pool, coolant supply means for supplying a coolant to saidcoolant pool through said hollow shaft, an inner shielding member formedof a cylindrical non-magnetic body and provided so as to surround thefield winding, a cylindrical outer shielding member disposed so as tosurround the inner shielding member and connected between said flangeportions, said outer shielding member being a cylindrical single-layerbody, coolant discharge means for collecting said coolant from saidcoolant pool through said hollow shaft, and a power lead passing throughsaid hollow shaft for supplying said field winding with electric power,wherein said outer shielding member is made of a non-magnetic nickelalloy substantially containing 0.05 to 0.25% carbon, 0.01 to 0.5%silicon, 0.01 to 0.5% manganese, 0.1 to 0.6% titanium, x% aluminum, y%copper, and the balance nickel by weight, where said aluminum content xand copper content y lie in a composition range having as cornersthereof a composition A (containing 2% aluminum and 12% copper), acomposition B (containing 2.5% aluminum and 40% copper), a composition C(containing 4.2% aluminum and 40% copper), a composition D (containing8% aluminum and 20% copper), a composition E (containing 8% aluminum and10% copper), a composition F (containing 7% aluminum and 8% copper), anda composition G (containing 4.5% aluminum and 8% copper), said alloyhaving such structure that a γ'-phase precipitation is formed by agingin an austenitic matrix.
 6. An electric rotary machine having asuperconducting rotor as claimed in claim 5, wherein said cylindricalsingle-layer body is a body which has been made through electroslagremelting.
 7. An electric rotary machine having a superconducting rotoras claimed in claim 5, wherein said outer shielding member has aresistivity of 70 μ5/8.cm or less and a proof stress of 60 kg/mm² ormore, at 20° C.
 8. An electric rotary machine having a superconductingrotor as claimed in claim 5, wherein said driving shaft is connected toa prime mover.
 9. A generator having a superconducting rotor, whereinsaid superconducting rotor comprises a driving shaft having at an endthereof a flange portion and adapted to be connected to a prime mover, ahollow shaft confronting said driving shaft with a gap therebetween andhaving a flange portion confronting said flange portion of said drivingshaft, a torque tube bridging a gap between said flange portions, afield winding supported on an outer peripheral surface of said torquetube, a non-magnetic holding sleeve adapted for holding the entireperipheral surface of said field winding, a coolant pool formed on theinner side of said torque tube, coolant supply means for supplying acoolant to said coolant pool through said hollow shaft, an innershielding member disposed as to surround the field winding, supported bysaid torque tube, and made up of a cylindrical non-magnetic innershielding body and non-magnetic reinforcing bodies closely fitted toinner and outer peripheral surfaces of said inner shielding body, acylindrical outer shielding member disposed as to surround the innershielding member and connected between said flange portions, said outershielding member being a cylindrical single-layer body, cooling ductsstarting from said cooling pool and extending along end portions of saidtorque tube and said outer shielding member, coolant discharge means forcollecting said coolant from said cooling ducts through said hollowshaft, and a power lead passing through said hollow shaft for supplyingsaid field winding with electric power, and wherein said outer shieldingmember is made of a non-magnetic nickel alloy containing 0.05 to 0.25%carbon, 0.01 to 0.5% silicon, 0.01 to 0.5% manganeses, 0.1 to 0.6%titanium, 2.5 to 6.0% aluminum, 9.2 to 15.0% copper, and the balancenickel by weight, said alloy having such a structure that a γ'-phaseprecipitation is formed by aging in an austenitic matrix. .Iadd.
 10. Arotor for an electric rotary machine, comprising a cylindrical shieldmember surrounding a field winding, said cylindrical shield member beingmade of a non-magnetic nickel alloy containing 0.05 to 0.25% carbon,0.01 to 0.5% silicon, 0.01 to 0.5% manganese, 0.01 to 0.6% titanium, 2.5to 6.0% aluminum, 9.2 to 15.0% copper, and the balance nickel by weight,said non-magnetic nickel alloy having such a structure that a γ'-phaseprecipitation is formed by age-hardening in an austenitic matrix, andsaid non-magnetic nickel alloy has a resistivity of 70 μΩ.cm or less anda 0.2% proof stress of 60 kg/mm² or more, at 20° C. .Iaddend. .Iadd.11.A rotor as claimed in claim 10, comprising a further cylindrical shieldmember surrounding said field winding, said further cylindrical shieldmember being interposed between said cylindrical shield member and saidfield winding. .Iaddend. .Iadd.12. A rotor as claimed in claim 11,wherein said further cylindrical shield member is made of a non-magneticmaterial. .Iaddend. .Iadd.13. A rotor as claimed in claim 11, whereinsaid field winding is provided on the outer peripheral surface of atorque tube. .Iaddend. .Iadd.14. A rotor as claimed in claim 13, whereinsaid torque tube has a coolant pool formed therein, with coolant supplymeans for supplying a coolant to the coolant pool and coolant dischargemeans for collecting coolant from the coolant pool. .Iaddend. .Iadd.15.A rotor for an electric rotary machine, comprising a cylindrical shieldmember surrounding a field winding, said cylindrical shield member beingmade of a non-magnetic nickel alloy containing about 0.15% carbon, about0.4% titanium, about 4.3% aluminum, about 20.7% copper, and the balancenickel by weight, said non-magnetic nickel alloy having such a structurethat a γ'-phase precipitate is formed by age-hardening in an austeniticmatrix, and said non-magnetic nickel alloy has a resistivity of about 53μΩ.cm and a 0.2% proof stress of about 78 kg/mm², at 20° C. .Iaddend..Iadd.16. A superconducting rotor for an electric rotary machine,comprising a cylindrical shield member surrounding a field winding, saidcylindrical shield member being made of a non-magnetic nickel alloycontaining about 0.16% carbon, about 1.2% titanium, about 2.7% aluminum,about 13.8% copper, and the balance nickel by weight, said non-magneticnickel alloy having such a structure that a γ'-phase precipitate isformed by age-hardening in an austenitic matrix, and said non-magneticnickel alloy has a resistivity of about 42.1 μΩ.cm and a 0.2% proofstress of about 61 kg/mm², at 20° C. .Iaddend. .Iadd.17. An electricrotary machine comprising: a field winding; a winding support shaft forsupporting said field winding; a torque tube for supporting said windingsupport shaft, a power lead for supplying electric power to said fieldwinding; at least one cylindrical shield member surrounding said fieldwinding; and a driving shaft fixedly connected to said at least onecylindrical shield member and said torque tube to thereby transmittorque through said torque tube and said winding support shaft to saidfield winding, wherein said at least one cylindrical shield member ismade of a non-magnetic nickel alloy containing 0.05 to 0.25% carbon,0.01 to 0.5% silicon, 0.01 to 0.5% manganese, 0.01 to 0.6% titanium, 2.5to 6.0% aluminum, 9.2 to 15.0% copper, and the balance nickel by weight,said non-magnetic nickel alloy having such a structure that a γ'-phaseprecipitate is formed by age-hardening in an austenitic matrix, and saidnon-magnetic nickel alloy has a resistivity of 70 μΩ.cm or less and a0.2% proof stress of 60 kg/mm² or more, at 20° C. .Iaddend. .Iadd.18. Anelectric rotary machine having a superconducting rotor which has ashield member made of a non-magnetic nickel alloy containing 0.05 to0.25% carbon, 0.01 to 0.5% silicon, 0.01 to 0.5% manganese, 0.01 to 0.6%titanium, 2.5 to 6.0% aluminum, 9.2 to 15.0% copper, and the balancenickel by weight, said non-magnetic nickel alloy having such a structurethat a γ'-phase precipitate is formed by age-hardening in an austeniticmatrix, and said non-magnetic nickel alloy has a resistivity of 70 μΩ.cmor less and a 0.2% proof stress of 60 kg/mm² or more, at 20° C..Iaddend.